do not fail when output directory does not yet exist

src/test/java/de/tudresden/inf/st/e2j/AbstractTest.java

@@ -8,19 +8,22 @@ public class AbstractTest {
 
   protected static void deleteFolder(String folder) throws IOException {
     Path directory = Paths.get(folder);
-    Files.walkFileTree(directory, new SimpleFileVisitor<Path>() {
-      @Override
-      public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
-        Files.delete(file);
-        return FileVisitResult.CONTINUE;
-      }
+    if (Files.exists(directory)) {
 
-      @Override
-      public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
-        Files.delete(dir);
-        return FileVisitResult.CONTINUE;
-      }
-    });
+      Files.walkFileTree(directory, new SimpleFileVisitor<Path>() {
+        @Override
+        public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
+          Files.delete(file);
+          return FileVisitResult.CONTINUE;
+        }
+
+        @Override
+        public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
+          Files.delete(dir);
+          return FileVisitResult.CONTINUE;
+        }
+      });
+    }
   }
 
 }